A composite material is a structural material that is made of two or more different materials. Cermet for example, is a composite material made of ceramic articles that are bonded with metal. Another type of widely used composite material is made of carbon fibers that are reinforced with an epoxy resin. It is this last type of composite material (i.e. carbon fiber/epoxy) that is of interest for the present invention.
Carbon fiber composite materials are unique in several aspects when they are used as a structural material. For one, unlike many other types of construction materials, they can be accurately pre-formed to assume complex shapes. For another, after they have been cured, they exhibit very good strength in both tension and compression. Carbon fiber composite materials, however, are typically made as relatively thin layers and, as such, they can be somewhat floppy. In many applications, this may be undesirable. The solution for such applications is to then somehow reinforce the layer of composite material in a manner that will stiffen and make the material rigid for its use as a support structure.
By structural analysis, it can be shown that a bending moment results wherever a force couple is applied to a structure. This bending moment can be resisted, however, when portions of the structure are distanced from each other and are located in the same bending plane, with a same center of bending. Indeed, the more material that is in the respective portions, and the greater the distance between them, the greater will be the structure's ability to resist bending. The well-known I-beam is a good basic example of such a structure.
Insofar as composite materials are concerned, and as noted above, although they may be formed as thin layers, and are therefore susceptible to being floppy, they typically have good strength characteristics in both tension and compression. Again, by way of example, an I-beam requires these strength characteristics. Heretofore, when a stiff, rigid structure has been required, and it has been desirable to use composite materials for its construction, it has been common to use two different layers of the composite material. The layers of composite material are then distanced from each other and interconnected by another structure, such as honeycomb. Unfortunately, even though composite materials and honeycomb are both relatively light-weight when compared with other structural materials, they still add weight. In the two-layer example considered above, the additional layer of composite material and the honeycomb may add substantial weight. For some applications (e.g. the manufacture of aircraft) weight limitation is of the utmost importance.
In light of the above, it is an object of the present invention to provide a reinforced panel, made of a composite material, that is sufficiently stiff and rigid to resist operational bending forces. Another object of the present invention is to provide a reinforced panel, made of a composite material, that is extremely light weight. Yet another object of the present invention is to provide a reinforced panel that is suitable for use as the external surface of a high performance aircraft. Another object of the present invention is to provide a reinforced panel that is relatively simple to manufacture, is easy to use and is comparatively cost effective.